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aapo lettinen

Is there a demand for custom sync sound motors?

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I became interested in microcontrollers a while ago and I am considering a DIY sync sound motor for my Kinor 2m camera. I also have other cameras which could use a stable speed motor (for example my 35mm Soyuz-US3N camera and the rheostat motored Konvas 1KCP. This is because there is no available motors of any kind for Soyuz and the rheostat Konvas never had any sync motors made originally) . 

I started with the 16mm Kinor motor last month and I'm refining the analog control electronics and fine tuning the code now. I was just thinking, is there lots of people out there who could use a customisable sync sound motor on their camera and if so, which exact camera models would be the most in demand?

If there seems to be some common interests then I could take them into account when developing my own motor project and it might be easy to make custom solutions for other persons cameras as well.

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What would be the absolutely mandatory specifications for this type of motor? I am aiming for +/- 10rpm accuracy at the moment but we will see how accurate the diy solution will be when it is fine tuned for the specific motor and camera model. That 10rpm accuracy would be about 1 frame drift for every 2.5 minutes of footage shot which should be usable for sync sound uses in indie films which have relatively short takes (a minute per take for example). My current design for the Kinor16 motor will have 6 different preset speeds and it uses the original pilot tone generator just like the Olex crystal sync modification does though my design is not as sophisticated or accurate (one gets what one pays for :) the Olex motor is better and my design is cheaper). 

- what type of camera and "wild" motor would most urgently need a digital speed stabilising system like this one?

- how accurate the speed needs to be. how much it can drift to be usable? I am talking about minimum specs which would enable practical use of the system, NOT about how much would be nice to have :)

- how much it can cost, in case there seems to be so much demand that it would be doable to do for example a dozen or so of these? 

- how much the end user can assemble by themselves? is a parts kit with pre drilled circuit board enough (needs soldering and a little bit of tuning) or only fully assembled board would do?

- it is very clear from beginning that this type of product needs to be user installed to be a viable option. It would not be economical to ship cameras and motors back and forth between continents, that would ruin the whole point of this type of motor solution 

- what kind of inputs for the encoder which is attached to the motor. My current design uses the pilot tone generator signal coming from the Kinor motor but for other cameras I will use either a encoder disc or magnetic sensors for rpm feedback. 

 

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continuing the project little by little. My current specs: 

- rotary switch for selecting 6 preset speeds. The speeds are specified directly in the program code and can be changed there. 

- a LED lights up when the selected speed is reached

- simple start-stop switch (can be wired to the original start-stop switch of the camera)

- input for AC pilot tone signal with simple setup to turn the signal to square wave for frequency metering

- the fine tuning of the speed control stability needs to be done setting the values directly in the code. this has to be done for every preset speed separately if the system is installed to different type of motor. basically testing how much the motor rpm oscillates around the set speed value and then manually tuning the pwm values to stabilise the rpm

- the board contains a protected output for motor pwm signal but the power transistors actually driving the motor are separate (some motors have suitable metal surfaces which can be used as heatsinks so it is more handy to make the control board small and figure out the power electronics placement case by case

 

- will add: output for using the frequency metering signal on external devices 

- will add: operational amplifier based, adjustable sensitivity input which could use optical and magnetic sensors for motor speed monitoring. 

- a possibility: dual operational amplifier inputs, both adjustable but one for encoder input and one with rectifier circuit to use with generators

- might happen or not: a small display to read information. this requires lots more coding and I will finish everything else first before attempting this

 

If anyone is interested in the project, please add comments and suggestions here or PM me. If there is a demand for this type of custom motor control electronics we can try to figure something out and maybe even do a small production run if it seems to be economically possible 🙂

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I would definitely be interested but I imagine the price point would be pretty high to make it worth your time.

I think the NCS Revolution Sync Motor sold for around 1K, not sure if they're still being made or not.

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1 hour ago, Webster C said:

I would definitely be interested but I imagine the price point would be pretty high to make it worth your time.

I think the NCS Revolution Sync Motor sold for around 1K, not sure if they're still being made or not.

I currently own three cameras which urgently need sync motors so I am primarily making the system for them. so small scale prototyping is not that costly and I have already done most of the hard work except the actual circuit board design (have to learn to use new programs so takes some time). The price point depends on how much the board needs customization or if the design I use fits the other cameras as well. Physical size is the most limiting factor if one wants to fit the whole system inside the existing motor housing. If an external box would do, then it would be much much simpler and cheaper.

One of the factors is that the current code needs to be fine tuned per camera/motor type and the end user may need to do this by themselves. The current system is based on Arduino so the fine tuning is very easy to do but it may not be for everybody and will take some time.

what will seriously take the cost up would be: 

- shipping cameras and motors back and forth, especially from U.S (installing by me instead of the end user) . By my opinion this should be avoided unless absolutely necessary

- small physical size which is more demanding on the circuit board manufacturing technology. Larger boards can be made by me at home by simple means but very small boards will probably need to be custom made in manufacturing company which necessitates very precise designing and standardizing and a larger production run which is not economical for this kind of relatively early prototype 

- custom manufacturing mechanical parts like encoder disc fittings. this may necessitate shipping the motor back and forth

 

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37 minutes ago, aapo lettinen said:

One of the factors is that the current code needs to be fine tuned per camera/motor type and the end user may need to do this by themselves. The current system is based on Arduino so the fine tuning is very easy to do but it may not be for everybody and will take some time

what it practically means is that one needs to open the program code in Arduino IDE , locate the lines which set the PWM cycle low and high values separately for every frame rate and then manually fine tune the low and high values when comparing how stable the set speed stays when changing the values. I may do this differently in future versions so it might change. The speeds are rpm in this version (the "freqSetVal" ) :

Quote


  if (freqSetVal==360.0){    // 6fps
    pwmValueLow = 40;
    pwmValueHigh = 120; }
    
  if (freqSetVal==720.0){   // 12fps
    pwmValueLow = 65;
    pwmValueHigh = 170; }

  if (freqSetVal==1438.56){   // 23.976fps
    pwmValueLow = 110;
    pwmValueHigh = 220; }
    
  if (freqSetVal==1440.0){   // 24fps
    pwmValueLow = 110;
    pwmValueHigh = 220; }
    
  if (freqSetVal==1500.0){  // 25fps
    pwmValueLow = 130;
    pwmValueHigh = 240; }

  if (freqSetVal==1920.0){  // 32fps
    pwmValueLow = 210;
    pwmValueHigh = 250; }

  if(digitalRead(STSTOP==HIGH){
    swModeA = true;  }
 

 

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9 minutes ago, Gregg MacPherson said:

Aapo, when you give tolerance at +/-10rpm, is it intended for cameras/motors with a 1 frame/rev relationship? If so that tolerance may be too great.

at this stage I am not absolutely sure how accurate the current design can be when it is properly fine tuned. The first working prototype could maintain about 50rpm accuracy so the 10rpm is a good target for now. Part of it is that the analogue electronics are not properly tuned yet and the square wave conversion is not perfect which messes up the speed calculations a little. The Kinor motor also generates one pulse per revolution which is not optimal for this type of system. With a proper encoder with dozens of slots the speed accuracy would be much better in any case but it needs lots of testing to see how accurate it can be

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24 minutes ago, aapo lettinen said:

what it practically means is that one needs to open the program code in Arduino IDE , locate the lines which set the PWM cycle low and high values separately for every frame rate and then manually fine tune the low and high values when comparing how stable the set speed stays when changing the values. I may do this differently in future versions so it might change. The speeds are rpm in this version (the "freqSetVal" ) :

 

It would be possible to attach a potentiometer on the board which could be used for fine tuning these values. but not every one of them... maybe one or two of the speeds closest together like the 23.976, the 24.00 and the 25.00 . That would actually help 90% of the users. I will consider that option 🙂

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7 hours ago, Tyler Purcell said:

What if the camera's movement makes so much noise you can't record sync sound anyway? 

then you add a blimp housing to the camera 😎

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design specs update, added features: 

- two trimmer potentiometers to easily fine tune the PWM values on the most critical mid range speeds (these are the 23.976, 24.00 and 25.00) . The fine tuning of the system on these speeds can be done with a screwdriver and no need to touch the code at all. The other speeds still need fine tuning to be really stable, especially the low speeds where high torque is generally needed 

- I will test off-the-shelf slot-type speed sensors to speed up the prototyping process a bit and standardize a critical part. If it works correctly, then a very common eBay sensor part can be used and it does not need preamplifier which makes circuit board designing much easier and would enable the end user to assemble all the mechanical parts of the system 

- function added to the program code which enables using a encoder disc with the system very easily. Just add the slot count of the disc to the code and it should work out of the box.

 

I have more time for prototyping next month. I will probably make a dedicated test motor for this project with custom diy made encoder disc. this way it is easier to finesse the speed control functions. I will probably use a motor of 10A to 15A power draw range which also helps testing the power electronics of the system.

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